The present invention relates to a radiographic image detection apparatus for exposing a patient to radiation so as to detect a radiographic image therefrom in radiation diagnosis.
FIG. 1 shows a conventional X-ray image detection apparatus which detects an X-ray image using an image intensifier (to be referred to as an I.I. for brevity) and an imaging tube. An X-ray tube 4 exposes a patient 2 to X-rays in response to an operation signal from an X-ray controller 12. The X-rays transmitted through the patient are radiated on an I.I. 6 which detects a transmission X-ray image. The I.I. 6 converts the X-ray image into an optical image and supplies the optical image to an imaging tube 10 such as a vidicon through an optical system 8. The imaging tube 10 converts the optical image into an analog video signal (time serial electrical signal), and the analog signal is converted into a digital signal by an A/D converter 18. Thereafter, the digital signal is supplied to an image memory 16. The memory 16 temporarily stores the digital video signal, and every time a predetermined amount of data is stored therein, supplies the storage data to an image processing unit 14. The unit 14 performs digital image processing such as digital subtraction. The digital signal generated from the unit 14 is converted into an analog signal by a D/A converter 20, and is then supplied to a TV monitor 22 to be displayed thereon.
However, the conventional X-ray detection apparatus using the I.I. and the imaging tube has the following drawbacks.
First, since the I.I. comprises a vacuum tube incorporating an electron lens, it is difficult to widen a detection field of view due to its structure. For example, in general, a maximum detection field of view of the I.I. is 12 inches (30 cm), and the shape thereof is limited to a circular shape.
Second, since the I.I. comprises a vacuum tube having a convex or concave surface, a pincushion distortion occurs in an output image. Even if an object having a uniform absorbency is imaged, the density distribution of an output image is not even, and so-called shading occurs at a peripheral portion of the image.
Third, since the imaging tube has a narrow dynamic range, it cannot be used both for fluoroscopy and radiography. In addition, due to its narrow dynamic range, the imaging tube has a low S/N ratio.